Positive-working radiation-sensitive coating solution and positive photoresist material with monomethyl ether of 1,2-propanediol as solvent

ABSTRACT

A positive-working radiation-sensitive coating solution is disclosed which contains a radiation-sensitive compound, e.g., a 1,2-naphthoquinone diazide, or a radiation-sensitive combination of compounds, e.g., a compound with at least one C--O--C bond which can be split by acid and a compound which upon radiation forms a strong acid, and at least one organic solvent which comprises a mono-C 1  to C 4  -alkyl ether of 1,2-propanediol. The coating solution is less toxic and results in a better layer leveling than known positive-working photoresist solutions.

This application is a continuation of application Ser. No. 742,063,filed June 6, 1985, abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a positive-working radiation-sensitivecoating solution which is particularly suitable for preparingphotoresist layers.

Positive-working photoresist solutions are known which are based onnaphthoquinone diazides or on a combination of compounds which can besplit by acid and compounds which, on exposure to actinic radiation,form a strong acid, respectively. Such photoresist solutions are widelyused in the production of printed circuits and microelectroniccomponents, and for chemical milling and the like.

In these applications, the photosensitive coating solutions are normallysupplied by manufacturers, and the users then apply the solutions to anappropriate layer support, for example, silicon wafers orcopper-laminated plates of an insulating material, whereafter the layersare dried. Such single coating methods are more difficult to perform andmore susceptible to trouble than the industrial coating of endlesssupports in continuous processes, which is customary in the productionof presensitized printing plates or dry resist films. When individualsupports are coated by the user, it is always more difficult to maintainexactly reproducible standard coating conditions.

The problems arising in this context are caused not only by the type andamount of the solid layer constituents but also to a considerable extentby the type of solvent (usually organic) employed. Since many users, whoonly coat small numbers of supports, do not possess installations for arecovery or environmentally safe disposal of the solvent vapors, onlysolvents which are not injurious to health are permitted. As standardsgoverning the use of organic solvents in laboratories have becomeconsiderably more strict in recent times, the choice of solvents hasbecome severely limited.

Nevertheless, most of the commercially available photoresist solutionsused in practice contain a solvent mixture. This is true because asuitable photoresist solution must dry to give a layer which is asuniform as possible and free from streaks, even when the temperaturesand drying conditions are not identical in all cases. Attempts toachieve this objective have usually involved providing a solvent mixturecomprised of several components, each having a different solvencycharacteristic relative to the layer constituents. Each component of thetypical solvent mixture also possesses a different evaporation number,so that a gradual solidification of the layer takes place in the courseof the drying process and inhomgeneities due to a premature separationof individual constituents are thereby avoided.

U.S. Pat. No. 3,634,082 teaches that ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, aliphatic esters (e.g., butyl acetate),aliphatic ketones (e.g., methyl-isobutyl ketone and acetone), dioxane,xylene and halogenated aromatic compounds (e.g., chlorinated xylene,benzene and toluene) are suitable solvents for positive-workingphotoresist solutions based on 1,2-quinone diazides. Essentially thesame solvents are employed for positive-working photoresist mixturesbased on compounds which can be split by acid, as described, forexample, in U.S. Pat. No. 4,101,323 and in European Patent ApplicationNo. 42,562.

In general, the main constituents of technical-grade photoresistsolutions are ethylene glycol derivatives, such as monomethyl andmonoethyl ethers, the corresponding ethers of diethylene glycol orethylene glycol ethyl ether acetate. These solvents display good solventpowers for all customary layer components, favorable boiling points andevaporation numbers, and reasonable prices. However, the layers obtainedusing these compositions are not in all cases faultless. Moreover, thepermissible values for their concentration in atmosphere of industriallaboratories have recently been reduced.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aphotoresist solution that employs solvents which compare favorably, withrespect to boiling point, vapor pressure, solvency characteristics andprice, to solvents used heretofore in the art, but that additionallyresults in improved layer qualities and fewer risks to health.

It is another object of the present invention to provide a photoresistdisplaying enhanced layer uniformity and a decrease in streaks.

In accomplishing the foregoing objects, there has been provided, inaccordance with one aspect of the present invention, a positive-workingradiation-sensitive coating solution comprising at least oneradiation-sensitive compound and an organic solvent which comprises amono-C₁ to C₄ -alkyl ether of 1,2-propanediol. In one preferredembodiment, the ether of the aforesaid coating solution is a monomethylether of 1,2-propanediol.

In accordance with another aspect of the present invention, there hasbeen provided a photoresist material comprising a support and alight-sensitive layer provided thereon, which light sensitive layer iscomprised of the above-described coating solution.

Other objects, features, and advantages of the present invention willbecome apparent from the following detailed description. It should beunderstood, however, that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The coating solution of the present invention contains a glycol etherwhich is a mono-C₁ to C₄ -alkyl ether of 1,2-propanediol. Preferably,the glycol ether is a mono-C₁ or C₂ -alkyl ether, particularly amonomethyl ether.

The alkyl ether group can be in the 1-position or in the 2-position ofthe propanediol. In the case of monomethyl ether, the more easilyaccessible 1-methoxy-propan-2-ol is generally preferred. It is alsopossible to use mixtures of the two methyl isomers and/or mixtures ofthe mono-C₁ to C₄ -alkyl ethers of propanediol.

The above-mentioned solvents are commercially available. Their maximumallowable concentrations in the ambient atmosphere of industriallaboratories are higher than the maximum concentrations of the ethyleneglycol ethers used to date. It is also of great advantage that, in manycases, coating solutions of the present invention which contain thesolvents mentioned above have more uniform leveling properties andprovide more homogeneous layers, especially if these solvents are theonly solvents used in the coating, than do solutions comprising thecorresponding ethers of ethylene glycol.

The advantageous properties of a coating solution within the presentinvention are retained when part of the propanediol mono-alkyl ether isreplaced by other customary auxiliary solvents, such as esters, likebutyl acetate; hydrocarbons, such as xylene; ketones, like acetone andbutanone; alcohols and certain alkoxyalkyl esters, e.g., 3-methoxy-butylacetate. If desired, the wetting, flow and evaporation characteristicsof the solution can be modified in this way on a case-by-case basis. Theadded amount of these additional solvents should in any event be lessthan 50% by weight. Preferably, their amount is 0 to 35% by weight, inparticular 0 to 20% by weight, relative to the weight of the solventmixture. Accordingly, the solvent or solvent mixture of this inventioncontains 65 to 100% by weight of a 1,2-propanediol mono-C₁ to C₄ -alkylether, preferably of a 1,2-propanediol monomethyl and/or monoethylether. In most cases, it is expedient to employ no other solvents exceptalkoxypropanol.

It is also possible to increase the flexibility of the layer by addinghigher-boiling alcohols or ethers, small quantities of which (forexample, about 1 to 2%) remain in the layer after drying. If desired,the rate of evaporation can be accelerated by adding a lower-boilingsolvent, such as, for example, sec-butanol.

The photoresist solution of the present invention can be applied in aknown manner to a support to be coated, for example, by immersion,slot-die-coating, spin-coating, spray-coating, roller-coating, orcurtain coating.

In most cases it is expedient to use no other solvent than thealkoxypropanol.

The total solids content of the solution according to the presentinvention generally varies between 10 and 50% by weight, preferablybetween 15 and 35% by weight, depending on the types of photosensitivecompounds and binders used in each case and on the intended use.

The coating solutions of the present invention also contain aradiation-sensitive (photosensitive) compound or combination ofcompounds. Positive-working compounds, i.e., compounds which arerendered soluble by exposure, are suitable for the present invention.They include 1,2-quinone-diazides and combinations of photolytic aciddonors and compounds which can be split by acid, such asortho-carboxylic acid compounds and acetal compounds.

Suitable 1,2-quinone-diazides are described, for example, in GermanPatentschriften Nos. 938,233 and 1,543,271, and in GermanOffenlegungsschriften Nos. 2,331,377, 2,547,905 and 2,828,037. Thepreferred 1,2-quinone-diazides are naphthoquinone-(1,2)-diazide-(2)-4-or -5-sulfonic acid esters or amides. Amongst these, esters, inparticular those of the sulfonic acids, are particularly preferred. Ingeneral, the quantity of 1,2-quinone-diazide compounds is 3 to 50% byweight, preferably 7 to 35% by weight, relative to the non-volatileconstituents of the mixture.

Coating solutions based on compounds which can be split by acid are alsoknown and are described, for example, in U.S. Pat. Nos. 3,779,778 and4,101,323, in German Patentschrift No. 2,718,254, and in GermanOffenlegungsschriften Nos. 2,829,512 and 2,829,511. The compounds whichcan be split by acid in such solutions include ortho-carboxylic acidderivatives, monomeric or polymeric acetals, enol ethers oracyliminocarbonates. As the compounds which are sensitive to radiationand which eliminate acid, the coating solutions predominantly containorganic halogen compounds, in particular s-triazines which aresubstituted by halogenomethyl groups or2-trichloromethyl-1,3,4-oxadiazoles. Among the orthocarboxylic acidderivatives described in U.S. Pat. No. 4,101,323, thebis-1,3-dioxan-2-yl ethers of aliphatic diols are particularlypreferred. Among the polyacetals described in German Patentschrift No.2,718,254, those with aliphatic aldehyde and diol units are preferred.

In German Offenlegungsschrift No. 2,928,636, very suitable mixtures arealso described which contain, as compounds which can be split by acid,polymeric ortho-esters with recurrent ortho-ester groups in the mainchain. These groups are 2-alkyl ethers of 1,3-dioxacylcoalkanes having 5or 6 ring members. Polymers with recurrent 1,3-dioxa-cyclohex-2-yl alkylether units, in which the alkyl ether group can be interrupted by etheroxygen atoms and bonded to the 5-position of the adjacent ring, areparticularly preferred.

The amount of compound which can be split by acid in the photosensitivemixture of the present invention is in the range of about 8 to 65% byweight, preferably between about 14 and 44% by weight, relative to thenon-volatile constituents of the mixture. The quantity of the compoundwhich eliminates acid is between about 0.1 and 10% by weight, preferablybetween about 0.2 and 5% by weight.

In addition to the above-described photosensitive constituents, thecoating compositions according to the present invention may containpolymeric binders. Preference is given to polymers which are insolublein water, but soluble or swellable in aqueous-alkaline solutions.

Suitable binders which are soluble or swellable in alkaline mediainclude natural resins, such as shellac and colophony and syntheticresins, such as copolymers of styrene and maleic acid anhydride orcopolymers of acrylic or methacrylic acid, particularly with acrylic andmethacrylic acid esters, and, in particular, novolaks. Of the novolakcondensation resins, the more highly condensed resins with substitutedphenols as the partners for condensation with formaldehyde have provedespecially useful. The type and quantity of the alkali-soluble resinscan vary depending on the intended use; preferably, the proportions ofthe resins in the total solids are 30 to 90% by weight, in particular 55to 85% by weight.

In lieu of, or in a mixture with, the novolaks, phenol resins of thepoly(4-vinyl-phenol) type can also be employed with advantage. Moreover,numerous other resins can be used in admixture. Preferably these arevinyl polymers, such as polyvinyl acetates, polyacrylates, polyvinylethers and polyvinylpyrrolidones, which again can be modified bycomonomers. The most advantageous proportion of these resins depends onthe technological requirements and on the influence on the developmentconditions desired. In general, the amount used should not be more thanabout 20% by weight of the alkali-soluble resin. To meet specialrequirements, such as flexibility, adhesion, gloss and the like, thelight-sensitive mixture can additionally contain small amounts ofsubstances, such as polyglycols, cellulose derivatives, such asethylcellulose, surfactants, dyes, and finely particulate pigments, andUV absorbers, if desired.

The solutions according to the present invention can be coated onto allsupport materials that are customary in photoresist technology, such ascopper-laminated plates of an insulating material, copper cylinders forgravure printing, nickel cylinders for screen printing, aluminum plates,glass plates, and the silicon, silicon nitride and silicon dioxidesurfaces employed in microelectronics. By applying the coating solutionsaccording to the present invention, for example, to plates of zinc,brass/chromium, aluminum/copper/chromium, aluminum or steel, it is alsopossible to obtain letterpress and offset printing plates.

Coated photosensitive materials exemplified above can be exposed bymeans of conventional light sources, the emission maxima of which are inthe long-wave UV range or in the short-wave visible range. Imaging canalso be effected using electron, x-ray or laser beams.

The aqueous-alkaline solutions which can be used for developing havegraduated alkalinity, i.e., they have a pH which preferably is betweenabout 10 and 14, and they can also contain minor amounts of organicsolvents or surfactants. Suitable developers remove those areas of thecopying layer which have been struck by light, and thus produce apositive image of the original.

The following examples illustrate preferred embodiments of the presentinvention. Unless otherwise stated, proportions and percentages denoteweight units. Parts by weight (p.b.w.) and parts by volume (p.b.v.) havethe same relationship as g and cm³.

EXAMPLE 1

This example illustrates the production by electroplating of rotarynickel screen printing stencils suitable for the printing of textiles.

A solution was prepared from

15 p.b.w. of butanone

45 p.b.w. of 1-methoxy-propan-2-ol (Dowanol PM, Dow Chem. Co., USA),

28 p.b.w. of a cresol/formaldehyde novolak having a softening range of105°-120° C. (according to DIN 53,181),

3.5 p.b.w. of polyvinyl ether (Lutonal A 25)

8.3 p.b.w. of the polyacetal of 2-ethylbutyraldehyde and triethyleneglycol,

0.2 p.b.w. of2-(6-methoxy-naphth-2-yl)-4,6-bis-trichloromethyl-s-triazine, and

0.01 p.b.w. of crystal violet base.

A 60 μm to 75 μm thick layer of good surface quality was coated onto abright, slightly contractible nickel cylinder provided with a conductivestripping layer, the coating being performed in two steps, with anintermediate drying step, by spray coating using compressed air. Therotating cylinder was then fully dried by means of infrared radiatorsfor about 30 minutes. The leveling time of the solution up to completedrying, as well as the layer thickness, could be varied by reducing thebutanone content of the solution. Even when the coating solutioncontained no butanone, a layer of good surface quality was obtained.

When a mixture comprised of 40 p.b.w. of butanone, 15 p.b.w. ofβ-ethoxy-ethyl acetate and 5 p.b.w. of 2-(β-ethoxy-ethoxy)ethanol wasused as the solvent for the above coating composition, the layer qualitywas also good. It was impossible, however, to achieve a layer of anequally good quality when one of the aforesaid solvents was used underpractical conditions.

The coated nickel cylinder was then appropriately exposed under apositive master of the pattern to be printed. The tonal values of themaster had been transformed into image portions of differing visualdensities by means of a screen having 32 lines per cm. Apositive-working layer based on 1,2-naphthoquinone diazide and havinghalf the thickness of the layer described above required four times moreexposure time. Development was performed with a solution of

0.5% of NaOH

0.8% of sodium metasilicate×9 H₂ O and

1.0% of ethylene glycol mono-n-butyl ether in

97.7% of deionized water.

For this purpose, the rotating, exposed cylinder was immersed in anappropriately sized vessel which had been half-filled with the developerliquid. The overdevelopment resistance of the layer prepared inaccordance with the present invention was very good, thus makingpossible the formation of steep resist edges. The cylinder was allowedto rotate in the developer for 6 minutes, after which the developervessel was removed and the cylinder rinsed with water and air-dried.

In the bared areas of the cylinder core, nickel was electrodeposited upto a thickness of 0.1 mm. Then the cylinder core was contracted, theresist stencil was stripped with acetone and pulled away from the core,and an elastic rotary printing stencil was obtained. Through the holesof the rotary stencil, ink was applied in imagewise manner to thetextiles to be printed.

Similar results were obtained when the polyacetal of n-heptanal andtetraethylene glycol was used as the acid-cleavable compound.

EXAMPLE 2

This example illustrates an application, by means of a roller coater, ofthe coating solution according to the present invention in theproduction of high-resolution printed circuit boards.

64 p.b.w. of the novolak of Example 1,

11 p.b.w. of polyvinylmethyl ether (Lutonal M 40),

15 p.b.w. of a polyacetal of 2-ethylbutyraldehyde and hexane-1,6-diol,

9.5 p.b.w. of the polyorthoester of trimethoxymethane and5-oxa-7,7-dihydroxymethyl-nonan-1-ol,

0.4 p.b.w. of 2-acenaphth-5-yl-4,6-bis-trichloromethyl-s-triazine, and

0.1 p.b.w. of crystal violet base

were dissolved in 1-methoxypropan-2-ol to give a solution having asolids content of 30%. A coating solution having a viscosity of about 90mm² /s was obtained. A corresponding solution with a solids content of40% had a viscosity of about 200 mm² /s. When the 1-ethoxy-propanol-2form (Ethoxypropanol EP, Deutsche BP Chemie GmbH) was used instead of1-methoxypropanol-2, the 40% coating solution had a viscosity of about320 mm² /s.

When a coating solution as described above was applied by rollerapplication, using a type AKL 400 roller coater (commercially availablefrom Messrs. Buerkle, Freudenstadt, Federal Republic of Germany) whichis suitable for double-sided coating and equipped with fluted rollershaving 48 or 64 flutes per 2.5 cm (linear), to through-hole platedcopper-laminated plates of an insulating material, dry layer thicknessesof about 3 to 14 μm were achieved in one coating step, depending on theresist solution, fluted roller and machine adjustment employed in eachcase. The leveling and drying times could also be influenced by anappropriate selection of 1-methoxy- or 1-ethoxy-propanol-2, or mixturesthereof, depending on the desired duration of the processing cycles.

The leveling and drying properties achieved with the above-describedcoating solution were good, comparing favorably to the propertiesobtained with the same mixture of solids dissolved in a conventionalsolvent mixture of β-ethoxy-ethyl acetate, xylene, β-butyl acetate and,optionally, an o,p-cholorotoluene mixture.

In accordance with a selective plating technique, the plate was exposedafter drying under a negative original which corresponded to the holeareas. The exposed areas were thereafter washed out with the developerof Example 1, and the plate was dried for 10 minutes at a temperature of80° C. The plate was then reinforced with copper by electroplating andtinned by electroplating. The photoresist layer was exposed under apositive conducting-path original and developed as described above. Thebared copper was then etched away with an alkaline etching agent.

If a softer consistency and higher flexibility of the photoresist layerwas desired, a mixture of 85% of 1-methoxy-propan-2-ol and 15% of2-ethyl-butanol could be employed instead of the single solvent usedabove. A small amount (up to 2%) of the higher-boiling solvent wouldthen remain in the layer after drying and act as plasticizer. Similarresults can be achieved by adding 10% of 3-methoxy-butanol or 20% of3-methoxybutyl acetate. 1-isobutoxy-propanol-2 (iBP, produced byDeutsche BP-Chemie) could also be used as an admixture constituent.

EXAMPLE 3

In an electrostatic spray device, a glass plate for the production ofLCD elements, which plate was provided with an indium-tin oxide layer,was coated with a solution comprised of

12 p.b.w. of the novolak of Example 1,

10 p.b.w. of a 50% strength solution of polyvinyl methyl ether intoluene, and

4 p.b.w. of the 1,2-naphthoquinone-2-diazide-4-sulfonic acid ester of4-(2-phenylprop-2-yl) phenol, in

74 p.b.w. of a mixture composed of equal parts of 1-methoxy-propan-2-oland 2-methoxy-propan-1-ol (Dowanol PM and Solvenon PM, made by BASF AG),

by the method described below:

A defined quantity of the coating solution was distributed by sprayingwith (1) a high-speed rotary bell, which had a diameter of 60 mm, and(2) a pump, at 40,000 rpm and 100 kV direct voltage. The bell wasarranged at a distance of 30 cm from the coating table, over which thegrounded glass plate was guided. Under the above-stated conditions, theflow of current was less than 1 mA. By varying the advance speed between0.8 and 2 m per minute and the rpm of the pump, dry layer thicknessesbetween about 4 μm and 10 μm could be obtained. When layer thicknessesof about 5 μm were desired, it was expedient to adjust the concentrationof the solution to 15%, if appropriate, by adding a higher-boilingsolvent.

After drying, exposure was performed under a positive originalrepresenting the feed lines of the display fields of a revolutioncounter. Development was then carried out with the solution of Example1, and finally the indium tin oxide was removed from the bared areas byetching with 5% strength hydrochloric acid.

EXAMPLE 4

The following positive-working photoresist solution was used forapplying high-resolution circuit patterns to a silicon wafer.

A solution containing

76 p.b.w. of 1-methoxy-propan-2-ol,

13.6 p.b.w. of the novolak of Example 1,

6.6 p.b.w. of1,3-bis-[2-(5-ethyl-5-butyl-1,3-dioxacyclohexoxy)]-2-ethyl-2-butylpropane,

1.1 p.b.w. of the triazine of Example 2, and

2.7 p.b.w. of polyvinyl ether (Lutonal A 25).

was applied to a silicon wafer by spin-coating at 6,000 rpm and dried ina circulating air cabinet to obtain a storable, positive-working,presensitized wafer. The light-sensitivity of the wafer was increasedseveral times over conventional positive-working photoresist layers ofthe same thicknesses which are based on o-naphthoquinone diazides. Acomparative test with the commercially available, o-quinonediazide-based photoresist AZ 1350J, which is widely used in the field ofmicroelectronics, was conducted under the same conditions as in Example1, except that a filter extending the exposure time was interposed,resulting in an exposure time of 3 seconds for the non-diazo layer andof 20 seconds for the diazo layer. The two exposure times were optimallyadapted for achieving good resolution up to about field 3/2 of the ITEKtest original, with a developing time of 1 minute in the developersolution of Example 1. Striation structures which may form during thespin-coating step could be avoided by adding a polysiloxane or fluorinesurfactant according to European Patent Application Nos. 42,104 and42,105, just as in the case of the AZ 1350J photoresist. A similarcoating quality is achieved when 1-ethoxypropanol-2 was used instead of1-methoxypropanol-2.

EXAMPLE 5

In the preparation of positive-working photoresist solutions forproducing autotypic copper gravure cylinders,

12 p.b.w. of the novolak of Example 1,

1 p.b.w. of a copolymer composed of 95% of vinyl acetate and 5% ofcrotonic acid,

2 p.b.w. of an ester mixture condensed from 1 mol of2,3,4-trihydroxybenzophenone and 2 mol of1,2-naphthoquinone-2-diazide-5-sulfonic acid chloride, and

0.1 p.b.w. of crystal violet base

were dissolved with stirring in

85 p.b.w. of 1-methoxy-propan-2-ol.

A comparison solution was prepared from

24 p.b.w. of the above novolak,

2 p.b.w. of the above copolymer,

4 p.b.w. of the above ester mixture, and

0.2 p.b.w. of crystal violet base, in

49 p.b.w. of trichloroethane,

14 p.b.w. of isopropanol,

7 p.b.w. of butyl acetate, and

100 p.b.w. of 2-ethoxy-ethanol,

and the two solutions were each applied, by means of a spray gun, tohalf of a freshly copper-plated rotating copper cylinder, respectively,until a layer thickness of about 4 μm was obtained. The layers were thendried with hot air or infrared radiators. When the two coated halveswere examined, it was found that the layer produced with the solution ofthe present invention was much smoother and more homogeneous, and hadbetter leveling characteristics, than the comparison layer. Therespective layers were then exposed under a half-tone negative of thepattern to be printed, and the copper surface was laid bare in imagewisefashion by pouring 0.8% strength sodium hydroxide onto the slowlyrotating cylinder. With the above-described layers, this process steptook 2 to 4 minutes. Thereafter, the cylinder was rinsed with water anddried with hot air while the cylinder was rotated.

Prior to the customary gravure etching with a solution of ferricchloride, the two layer portions to be compared were touched up bycorrecting them mechanically with a graver and by applying marks andadditional lines. With both layers, similarly, good results wereachieved, because after drying both layers still contain about 1% ofresidual solvent, which in the comparison layer essentially comprisedtoxic 2-ethoxyethanol.

EXAMPLE 6

This example illustrates the use of a coating solution according to thepresent invention in the production of an offset printing form.

A coating solution containing

7 p.b.w. of the novolak of Example 1,

2 p.b.w. of 2-(naphth-2-yloxy)-5,5-dimethyl-1,3-oxazolin-4-one,

0.4 p.b.w. of2-(4-methoxy-anthrac-1-yl)-4,6-bis-trichloromethyl-s-triazine, and

0.1 p.b.w. of 4-diethylamio-azobenzene, in

90.8 p.b.w. of 1-methoxy-propan-2-ol,

was applied, by roller coating, onto an aluminum substrate which hadbeen roughened on one side by means of wire brushes. The aluminumsurface was readily and uniformly wetted with the solution, and theapplied layer maintained its homogeneous character until it wascompletely dry. For an accelerated drying, up to 15% of the solventcould be replaced by sec-butanol. For a prolonged drying, all or part ofthe 1-methoxy-propanol-2 could be replaced by 1-ethoxy-propanol-2.

The resulting layer had a thickness corresponding to a weight of 2 g/m².

After drying, the plate was exposed under a positive original, developedwith a 3.5% strength aqueous solution of trisodium phosphate which had apH adjusted to 12.6 by the addition of sodium hydroxide, rinsed withwater, and finally made ready for printing by wiping with 1% strengthphosphoric acid. Even when the plate was left in the developer solution12 times longer than required for development, practically no defectswere apparent in the image areas. Thereafter, the plate was used forprinting, and it accepted ink very readily.

EXAMPLE 7

With the same solid components as in Example 1, dissolved in1-ethoxy-propanol-2 to give a 40% strength solution, a system suitablefor electrostatic spray coating under conditions similar to those ofExample 3 was prepared (bell distance 20 cm, high voltage 80 kV). Thesolution was first adjusted to a solids content of 26% by weight bydiluting it with 3-methoxy-butanol-1. After drying, the layer had aweight of about 5 g/m². On supports of aluminum and copper, the layerexhibited good leveling properties.

The resist solution could be used for spray coating even with aremarkably high solids content. The addition of up to about 5% ofisobutoxy-propanol was possible without a requisite change in the sprayconditions.

What is claimed is:
 1. A positive-working radiation-sensitive coatingsolution suitable as a photoresist, consisting essentially of, inadmixture, (i) at least one polymeric binder which is soluble orswellable in alkaline media and soluble in monomethyl ether of 1,2propanediol said binder being present in an amount between about 30 and90 percent by weight, relative to the total solids of said coatingsolution; (ii) a sufficient amount of at least one radiation-sensitivecompound to impart radiation sensitivity to said coating solution; and(iii) an organic solvent present in an amount sufficient to solubilizesaid binder, which organic solvent consists essentially of a monomethylether of 1,2 propanediol in an amount of between about 80% and 100% byweight of said organic solvent.
 2. A coating solution as claimed inclaim 1, wherein said radiation-sensitive compound is a1,2-naphthoquinone-2-diazide.
 3. A coating solution as claimed in claim1, comprising a radiation-sensitive combination of(a) a compoundcontaining at least one C--O--C bond which can be split by acid and (b)a compound which upon irradiation forms a strong acid.
 4. A coatingsolution as claimed in claim 1, wherein said polymeric binder comprisesa novolak.
 5. A coating solution as claimed in claim 1, wherein saidorganic solvent comprises 1-methoxypropane-2-ol.
 6. A coating solutionas claimed in claim 1, wherein said organic solvent consists essentiallyof said ether.
 7. A coating solution as claimed in claim 6, wherein saidorganic solvent consists of said ether.
 8. A coating solution as claimedin claim 1, said coating solution consisting essentially of saidcomponents (i), (ii) and (iii).
 9. A photoresist material, comprising asupport and a light-sensitive layer provided on said support, said layerbeing the product of a process comprising the step of coating saidsupport with a positive-working radiation-sensitive coating solutionwhich is suitable as a photoresist and which consists essentially of, inadmixture, (i) at least one polymeric binder which is soluble orswellable in alkaline media and soluble in monomethyl ether of 1,2propanediol said binder being present in an amount between about 30 and90 percent by weight, relative to the total solids of said coatingsolution; (ii) a sufficient amount of at least one radiation-sensitivecompound to impart radiation sensitivity to said coating solution; and(iii) an organic solvent present in an amount sufficient to solubilizesaid binder, which organic solvent consists essentially of a monomethylether of 1,2 propanediol in an amount of between about 80% and 100% byweight of said organic solvent, such that said light-sensitive layercontains, after drying, about 1% of said organic solvent.
 10. Aphotoresist material as claimed in claim 9, wherein said organic solventconsists essentially of said ether.
 11. A photoresist material asclaimed in claim 10, wherein said organic solvent consists of saidether.
 12. A photoresist material as claimed in claim 9, wherein saidorganic solvent comprises 1-methoxypropane-2-ol.
 13. A photoresistmaterial according to claim 9, wherein said organic solvent furtherconsists essentially of a second, higher-boiling organic solvent, suchthat up to 2% of said higher-boiling solvent remains in said layer afterdrying.